Mold drying and cooling oven



June 13, 1961 c. H. BARNETT EI'AL 2,988,351

MOLD DRYING AND COOLING OVEN Filed June 17, 1958 5 Sheets-Sheet 1 FIG. I

I6 I I 5 I5 a 34 INVENTORIS CHARLES H. BARNETT a FIG. 2 RBIEQHARD E. TEAGLE ATTORN E YS June 13, 1961 c. H. BARNETT ETAL 2,988,351

MOLD DRYING AND COOLING OVEN Filed June 17, 1958 5 Sheets-Sheet 2 INVENTORS CHARLES H. BARNETT 8: Y RICHARD E TEAGLE ATTOR NE Y5 June 13, 1961 c. H. BARNETT ETAL MOLD DRYING AND COOLING OVEN Filed June 17, 1958 5 Sheets -Sheet 3 FIG. 5

. INVENTORS CHARLES H. BARNETT 8: BY RICHARD E. TEAGLE aw M ATTORNEYS June 13, 1961 C. H. BARNETT EIAL MOLD DRYING AND COOLING OVEN Filed June 17, 1958 5 Sheets-Sheet 4 ATTORNEYS June 13, 1961 c. H. BARNETT ETAL 2,988,351

MOLD DRYING AND COOLING ()VEN Filed June 17, 1958 5 Sheets-Sheet 5 FIG. 8

INVENTORS CHARLES H. BARNETT a FIG. 9 BY RICHARD E.TEAGLE ATTORNEYS United States Patent 2388351 MOLD DRYlNG AND COOLING OVEN Charles H. Barnett, Shaker Heights, and Richard E.

Teagle, Pal-ma, Ohio, assignors to The Foundry Equiplgfilt Company, Cleveland, Ohio, a corporation of Filed June 17, 1958, Ser. No. 742,683 8 Claims. (Cl. 263-40) This invention relates as indicated to a mold drying and cooling oven, and more particularly to an oven especially adapted to handle very large molds.

It has long been recognized as a diflicult problem to dry sand molds properly in a short period of time, with the various factors making such an operation difficult to attain being of course especially evident in the treating of very large molds, which may, for example, be on the order of fourteen feet square. Such large molds are not well adapted for drying in continuous conveyor ovens, and consequently it has been the usual practice to dry such molds by means of manually applied gas torches, to build charcoal fires under them, and to close the molds and connect portable dryers thereto. Very large castings cannot be conveniently surface cleaned as may small castings, by tumbling, for example, and it is therefore often preferred to employ dry sand molds for large castings, particularly when pouring very hot metals such as steel, in order to obtain a good smooth surface without sand inclusions, etc. For these and other reasons, we employ an oven into which the molds may be moved on cars or conveyors for action of drying gases thereon for a predetermined period of time prior to removal.

It is generally necessary to place cores in the molds after completion of the drying operation and in view of the large size of such molds it has been found necessary for the workman to wait quite a long period of time, often several hours, before the molds have cooled sufiiciently to permit performance of such further operations thereon. It is accordingly an important object of our invention to provide ovens particularly suited for the drying of large molds and which are also adapted quickly and efliciently to cool such molds before removal of the same.

Another object is to provide an oven of the type indicated wherein the heating and cooling cycles may be alternated quickly and with a minimum loss of heating efiiciency.

Still another object is to provide a method of dryin molds which will skin dry the same to a substantial depth (e. g. one-half inch to one inch or more) by removal of moisture from the surface layer so that such surface layer will remain dry enough for pouring of the casting metal in the mold even if the mold should be allowed to stand for a period of some hours prior to pouring; this being in contrast to prior art procedures tending principally to drive surface moisture back into the body of the mold from which region it subsequently tends to return to the surface layer with relative rapidity.

A still further object is to provide an oven and mold arrangement whereby both a cope and drag mold may be dried simultaneously.

Another object is to provide a mold drying oven in- Patented June 13, 1961 ings setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principle of the invention may be employed.

In said annexed drawings:

FIG. 1 is a partially fragmented side elevation of one oven embodying our invention;

FIG. 2. is a plan view of such oven, with certain support pieces being omitted for clarity;

FIG. 3 is a front elevation of this oven;

FIG. 4 is a transverse section as viewed from the plane indicated by the line 4-4 in FIG. 1;

FIG. 5 is a vertical longitudinal section the plane of which is indicated by the line 5-5 in FIG. 2;

FIG. 6 shows another embodiment of the invention in a vertical longitudinal section, the plane of such section being indicated by the line 66 in FIG. 7;

FIG. 7 is a plan view in partial section of the oven illustrated in FIG. 6;

FIG. 8 is a section approximately on the line 88 in FIG. 7; and

FIG. 9 is a schematic diagram illustrating a safety control circuit for the ovens.

Referring now to the drawings in detail, the embodiment of the invention illustrated in FIGS. 1 to .5 is a car-type mold oven 10. and is thus supported on the floor, for example, the floor 11 of the plant in which the oven is located. The walls forming this oven are either insulative or insulated in appropriate manner and so proportioned that the work-receiving compartment is elongated and open at one end.

With such construction, the molds are of course insertedin the oven and withdrawn at the same end; the particular plant organization may make it more appropriate for the work to move completely through the oven and in this case a discharge opening would be provided, with a suitable closure, at the other end.

The. opening 12 at such end extends to the floor 11 and adoor 13 movable vertically in angle guides 14is provided to open and close the same. A motorized door lift is used, this mechanism here comprising a pair of cables 15 attached to a top flange 16 of the door and extending upwardly to an elevated cross frame 17 supported by the door guides 14 and other suitable structural members, such as the strut 18. Each cable is trained over-a drive pulley 19 mounted on a shaft 20 journalled eluding provision for subsequently cooling the mold, such,

cooling means making use of much of the heating. and

drying system of the oven with a minimum of additional.

equipment.

Other objects of the invention willappear as the description proceeds.

in blocks 21 at the top of the cross frame and driven by an electric motor 22, likewise supported by such frame. The cables then pass over rear pulleys 23 and hang from the latter with counterweights 24 attached at their other ends. Appropriate controls, not shown, are of course provided forconvenient actuation of this motorized door lift by an operator of the oven.

L The floor within the oven is formed with a longitudinal depression 25 which. extends centrally from the rear wall substantially to the front of the oven, as shown clearly in FIGS. 4; and 5, for a purpose to be described. Rails 26 are embedded in the floor respectively closely adjacent the sides of the depression, at normal floor elevation, and such rails extend through the open end or ends of the oven and to such point or points as may be appropriate in the particular plant to form a track along which a conventional mold-supporting car 27, shown in phantom in the same figures, may be moved to carry the molds to and from'the oven.

i 1 The heater for the oven is indicated generally by reference numeral 28 and is supported above the top thereof by a frame which includes longitudinal side channels 29 secured to the top wall and a series of transverse I-beanis 30. Such heater comprises a casing 31 and. a gas andoil fired burner assembly 32 of conventional construction arranged so that its flame projects into the casing to contact and thus heat air circulated through the same. Such air is withdrawn from the heater 28 through a large opening 33 in an end wall thereof, and a similarly large conduit section 34 connected to the inlet of a supply fan 35. The conduit section is of elbow shape, with an upper lateral connection to the fan and an opening 36 at its top in which a control damper 37 is provided.

The supply fan 35 is thus-spaced somewhat above the top of the heater for increased clearance between the same and the top of the oven, and it is driven by an electric motor 38 connected to its shaft 3-9 through a belt and pulley system 40. The inlet connection is at the eye of the fan and the usual scroll housing terminates in a downwardly directed discharge or outlet 41. Such outlet section is almost immediately laterally enlarged and divided centrally by a duct section of general inverted V- shape the branches of which are indicated at 42 and 43, respectively. A damper 44 is pivoted at the lower junction of such branches and stops 45 and 46 are secured to the inner upper surfaces of the latter at such opposed locations that the damper when brought against each stop completely closes the branch in which the same is operative.

As will be seen most clearly from FIG. 5, the damper 44 can then be actuated to direct all of the discharge from the supply fan 35 to either branched outlet or variably divide the discharge between the two. Since the fan is oriented transversely with respect to the oven, these branches are directed respectively to the front and rear of the oven and the branch 42 at the front, relatively speaking, is enlarged toward the sides of the oven and divided at its lower surface into two downwardly directed sections 47 and 48 which extend through the top of the oven in spaced side-by-side arrangement. A small damper 49 is provided to pivot along the inner line of divergence of such sections and is thus operable to eifect the distribution of the flow to the same.

These two duct sections 47 and 48 extending through the top of the oven communicate respectively with a pair of ceiling ducts 50 and 51 which extend substantially from the front to the rear of the chamber in spaced parallel relation. The bottom wall of each such ceiling duct is formed with a multiplicity of downwardly directed discharge nozzles 52, whereby a downward flow of air over substantially the entire ceiling area may be established. Such discharge of heated air will be discussed further hereinbelow in connection with the over-all operation of theoven.

The rear branch 43 at the outlet of the supply fan 35 is connected by a transition duct section '53 to a relatively wide and narrow duct 54 extending downwardly into the oven along the rear wall of the same to the central longitudinal depression 25 of the floor. At its lower end, this vertical duct is divided laterallyinto two sections 55 and 56, with a further damper 57 across the inner junction for divisive regulating effect on the flow. There is a central partition 58 in the depression 25 and at each side of the same there is a floor duct 59 connected to one of the terminal sections of the vertical supply duct. Such partition is made of insulating material and is here used to position car-moving mechanism (not shown) away from the floor ducts to reduce heat transfer thereto. Where such mechanism is not used, or where other non-obstructive means shields the same, there is obviously no need to provide the partition and two separate floor ducts and a single such duct of substantially the same width as the depression will be substituted. The upper surfaces of such floor ducts are formed with upwardly directed nozzles 60, so that there is an'upward, as well as downward, discharge of air in the work-receiving compartment. As illustrated, the depth of the depressed area in which these floor ductsare located and; the height of thelatter, including the nozzles, are .so related that the tips of ,the nozzles are substantially at the normal floor elevation.

In order to recirculate air from the oven, a return or collector duct 61 is disposed in each upper corner of the heating chamber, these ducts being outboard of the celling supply ducts and having adjustable inlets 61a at the bottom. At a forward region of the oven, approximately coincident with the forward end of the superimposed heater, such return ducts are connected through the oven roof to the ends of an external transverse duct 62. A stack 63 is connected to such transverse duct, with, however, a recirculating duct 64 connected between a lateral opening 65 in the stack and the end of the heater 28 opposite the end thereof to which the heat supply fan 35 is connected. A damper 66 is, moreover, pivoted at the upper edge of the opening from the stack to the recirculating duct, and this damper can be moved between a vertical position, in which the recirculating duct is closed to the stack and a horizontal position, with its free margin against a stop 67, in which the upper portion of the stack is completely closed. It will thus be seen that this damper is operable to provide a complete recirculation of the oven air collected in the return ducts 61 or full exhaust of the same.

It is desirable, for efficient operation, that a certain quantity of the air in the oven be continuously and completely exhausted, and this is conveniently accomplished in the illustrated oven by means of an external exhaust duct 68 a ceiling exhaust duct 68a having adjustable air inlets 68b, an exhaust fan 69 driven by a further electric motor 70, and a main stack 71.

The interior exhaust duct 68a is formed by closing the bottom of the longitudinally extending space between the two ceiling supply ducts 50 and 51 and, as shown, air proceeds from the same through the exterior exhaust duct 68 to the fan 69 and out the stack 71. Such discharge is of course independent of the recirculating duct system described, and the amount of air thus withdrawn will be proportioned with due regard to the size of the oven, the expected work load, etc. The heater 28 will be regulated to draw in a corresponding flow of fresh air from the atmsphere by conventional adjustment to make up such loss.

As previously stated, this oven is designed not only to heat the work for drying but also to cool the same quickly and efliciently before removal, and a full cycle of heating and cooling will now be described. Referring first to the phantom outline shown in FIG. 4, the cope and drag molds 72 and 73 carried by the car 27, which is of the usual skeleton construction, are preferably supported back-to-back so that the cope mold cavity faces downwardly to the floor of the oven and the drag mold cavity faces upwardly toward the ceiling. With the various dampers occupying the full line positions thereof shown in FIG. 5, the heat supply and exhaust fans are set in operation and the burner is fully ignited.

vAs shown by the arrows, the air heated by the burner 32 is drawn through the elbow section 34 to the supply fan35 and discharged by the latter into the branches 42.

and 43. Approximately half of this discharge is thus directedto the ceiling ducts 50 and 51, being divided therebetween by the connecting duct sections 47 and 48, and this portion of the flow is forcibly directed by the nozzles 52 downwardly into the oven and against the work, in thiscase, the upturned drag mold.

The other half of the supply of heated air proceeds from the branch 43 through the transition 53, and the ductwork 54, 55, 56 to the floor ducts 59, which extend beneath the car. Accordingly, heated air is also discharged upwardly against the downturned cope mold by the nozzles 60. V

Return air from the oven is drawn into the side ducts 61 and flows through the lower portion of the stack 63 and the recirculating duct 64 to the heater 28 for passage therethrough and reheating therein back'tothe" supply fan 35 and recirculation. The exhaust fan 69 will of course extract the predetermined small portion of the oven air which is to be completely exhausted through the main stack 71, with this loss being made up by the make-up air and gases of combustion respectively drawn in by and delivered from the heater.

When the molds have thus been suiliciently "dried, the oven is then adjusted to provide the desired cooling cycle by turning off the'main fire of the burner (leaving the .pilot on), opening the damper 37, and shifting the damper 66 in the stack to its dashed line vertical position shown in FIG. 4. Fresh air will consequently be drawn in by the fan 35 through the opening 36 in the elbow 34, in eflFect short-circuiting the heater, and forced thereby into the oven through theceiling and floor ducts in the same manner as in the heating cycle. Air from within the oven again escapes into the side ducts 61 and the stack 63, but the recirculating duct 64 to the heater is closed in this condition and accordingly suchair passes out this stack, the small, constant exhaust provided by the exhaust fan 69 continuing unchanged.

It will be noted that there is no fan in the cooling stack 63, reliance being placed on the supply fan to push air out of such stack in the cooling cycle, so that the oven is definitely under positive pressure in this cycle of operation. In the heating cycle, on the other hand, the continuous exhaust and the corresponding intake of make-up air are usually so small in proportion to the recirculation that the oven is placed under negative pressure, which is generally desirable since any leakage, for example, at the door, will constitute flow from the outside into the oven, rather than escape of the gases within the same. Such change in oven pressure in the two cycles is obviously relative, but in all contemplated operation, the oven will be placed under more positive pressure during cooling than obtains in the heating or drying cycle.

In this manner the molds are quickly and eificiently cooled before removal, with the conversion of the oven from one cycle to the other being accomplished obviously with relatively easy and rapid adjustment. Particular load conditions which desirably call for some unevenness in the discharge of the air within the oven, Whether in the heating or cooling cycle or both, can be met by appropriate adjustment of the various distribution dampers, the dampers 49 and 57 for example, being adjustable to direct more air to one side of the oven than the other. The distribution between the ceiling and floor discharges is also variable, and only one such discharge may be used where this would be more desirable and economical for treating a given load. Adjustment of the various inlets of the return and exhaust ducts provides uniform flow of oven air into the same throughout the extent thereof, so that the collection of such air is likewise balanced.

The further embodiment of the invention illustrated in FIGS. 6 to 8 is operative to provide the same heatingand cooling cycles, but utilizes a different construction which would be more suitable for a smaller size oven, for example, one designed to treat a single cope or drag mold at a time. This oven 74 is supported on the floor 75 of the plant and is elongated, with an access opening 76 at one end and a vertically movable door, 77 closing the same. For convenience, the door lift mechanism has not been here illustrated in detail; due to the reduced size and hence weight of the door, it may be unnecessary to provide a motor drive, relying instead on counter-balancing and manual lifting. As with the oven first described, the material flow in the plant may make it more advantageous to provide openings at both ends.

In this further construction, the opening 76 for access to the oven does not extend completely to the floor and a roller conveyor 78 extends suitably within the plant to the oven, with its upper carrying surface slightly above the bottom edge of the door opening adjacent the same. A further roller section 79 is provided in the oven, extending longitudinally therein from the front substantially to the rear and forming effectively a continuation of the external conveyor.

' 6 A large mixing chamber is provided on the top of the oven, and supply fan 81 is mounted therewithin.

.Heater unit 82 is arranged with its combustion zone in the chamber. An opening 86 is provided in the front end wall of such chamber and a door 84, operable by a double-acting aircylinder 85, opens and closes this chamber opening. The supply fan is driven by an elec tric motor 86 located outside the chamber and its outlet 87 extends downwardly through the oven top to a central ceiling duct 88 with downwardly projecting nozzles 89 as shown, no floor duct being provided in this particular oven. Completely surrounding the central supply duct, there is a return duct 90 having adjustable inlets 90a, and it will be noted from FIGS. 7 and 8 that the mixing chamber 80 is off-set to one side at the top of the oven, so that it is positioned above the return duct portion at such side.

Communication between the duct 90, at this portion thereof, and. the mixing chamber 80, is provided by an opening in the top of the duct, and an opening 91 in the oven top in registry therewith. A damper 92, likewise having adouble-acting air cylinder 93 for control of the same, is mounted in this top oven opening to close and open the same. At the front of the oven, a cooling stack 94 is connected to the interior duct 90 and a damper 95 is provided to open and close such stack slightly above the level of the oven roof; this damper also has an air cylinder 96 connected thereto for automatic control. The constant exhaust of a small portion of the air in the oven is accomplished in this construction by means of a vertical exhaust duct 97 extending from another portion of the oven duct 90, to an exhaust fan 98 driven by an electric motor 99 and having its outlet connected to a main stack T00. As before, the relatively small portion of the gases withdrawn by the exhaust fan is made up by the make-up air and combustion products respectively drawn in by and delivered from the heater.

The mold should be rolled into this oven with its cavity facing upwardly toward the nozzles 89 and to dry the same, .door 84 is closed, damper 92 opened, and damper 95 closed. With the two fans running, the burner is turned to main fire and heated air will. be forced into the central ceiling duct 88 and discharged downwardly against the mold by the nozzles 89. With the exception of the small amount extracted by the exhaust fan 98, the air is drawn from the oven into the peripheral duct 90 and through the opening 91 into the mixing chamber 80 for reheating and recirculation.

To shift the oven to the cooling cycle, the burner being turned down as before, the door 84 and damper 95 are opened and the damper 92 for recirculation is closed. Accordingly, fresh air is taken into the mixing chamber by thesupply fan 81 through the opening 83 thereto and the major portion of the air within the oven is forced out the cooling stack 94, the remainder being exhausted through stack 100 by the relatively small exhaust fan. Once again the. oven is under negative pressure during the heating cycle and positive pressure in the cooling cycle, the consideration discussed heretofore in this regard being applicable here as well.

We have shown pneumatic means susceptible of auto.- matic control for actuating the control dampers in this further embodiment of our invention to illustrate a form of system employed for the regulation of the oven, and it will be clear that the first-described oven will similarly be provided with suitable controls. Such a system will include as well the various interlocked circuits and other safety devices used to protect against improper operation, such as may result from burner ignition failure, excessive heating of the supply fan, and the like.

Basically, however, once the oven is started properly, in both forms of the invention described, the alternation between heating and cooling cycles will be seen to involve only relatively minor changes in the set-up due to the fact that our construction involves a minimum of components which are usable only in one cycle or the other. The manner in which a low level exhaust is prof'vided independently of the recirculating means greatly simplifies the control of the latter, with all major adjustments being merely shifts between on-off or openclosed conditions.

' I As earlier indicated, the burner is of conventional construction and it will be equipped with means for providmg low and high fire settings by regulation of the fuel supply thereto. When igniting the burner, with a usual ignition device, the low fire setting should obviously be used for safety, and since the normal operation of our oven involves alternation between heating and cooling cycles, with the burner being turned on and off, we have provided a control feature whereby the burner is automatically adjusted to and maintained in the low fire position during the cooling cycle, so that there is no danger -of maximum fuel flow upon re-ignition in a subsequent heating cycle.

The schematic diagram of FIG. 9 serves to illustrate thiscontrol, with the burner being shown at B and the fuel mixture supply being represented by the pipe 101. In such pipe, there is shown a solenoid-actuated valve 102 having its coil connected to a suitable source of energy indicated by the conductors L and L through a switch 103. A second valve 104 is positioned in the line between the burner and valve 102 and such further valve modulates the flow to establish the low and high fire conditions mentioned. Valve 104 is actuated between suchpositions of adjustment by a small electric motor 105 which is here unidirectional and also operates certain switches of a control circuit coincident with movement of the valve 104 from one setting to another. One side of the motor is connected directly to a line conductor L by a wire 106, and there are several circuits for connecting the other side of the motor to the conductor L to complete energization of the same. These circuits include switches operated by a temperature controller and switches for shifting between the heating and cooling cycles of oven operation, as well as the noted motoroperated switches.

The motor-operated limit switches are designated 107 and 108, respectively, with a common actuator 109 there for, drivenby the motor. The temperature controller has been indicated by a bi-metal strip 110 having a con- 'tactor 111 movable between positions respectively closing switches 112 and 113. The switches for shifting between the heating and cooling cycles are shown at 114 and 115, with an actuator 116 therebetween, and this actuator J's-preferably ganged, either mechanically or electrically, with the switch 103 for movement in unison therewith in a-manner which will be apparent in the following. .The main returnwire to the conductor L is designated 117, and the remaining wires interconnecting the various switches can best be identified in describing the operation of the control.

In the condition of operation illustrated in the diagram, a heating cycle is in progress and the burner is set on main or high fire. Switch 103 is thus closed to open the main valve 102, motor 105 has fully opened and modulating valve 104 and moved the switch actuator 109 to close the switch 108. The temperature within the oven is "below the operating value for which the temperature controller -110has been set and such controller has operated to close the switch 113; Cycle shift switch 114 .is closed by actuator 116, along with switch 103, throughout the heating cycle. The motor 105 is, at the given moment, .de-energized. When the oven nowattains the operating temperature for which the controller has been set, the same operates to open switch 113 and close switch 112. This completes the motor circuit from conductor L wire 106, the motor, wire 118, switch 112, wire 119, switch 114, wire i120, switch 108, wire 117, and the conductor L The motor is thus energized and shifts the valve 104 from the high to the low fire adjustment and, upon reaching such new setting, switch 108' is opened by the motor to inter- 8 rupt its energization circuit and switch 107 is closed. The motor then stops and the burner now operates at low fire until the oven temperature drops enough to cause the temperature controller to open switch 112 and close switch 113. When this happens, the motor is again energized by another circuit comprising the now-closed switch 107, wire 120, switch 114, wire 119, switch 113, wire 121 and return wire 117. Running of the motor moves the valve 104 to high fire position and operates also to open switch 107 and close switch 108, so that the first described condition again exists. It will be understood that this regulation of the fuel supply will continue throughout the heatingcycle in accordance with the oven temperature.

At the completion of the predetermined time for heating or drying, switch 103 is opened to close valve 102 and thereby shut olf the burner, the pilot of course remaining lit. The various dampers are actuated in the manner aforesaid and actuator 116 moves to close switch 115, this last action opening switch 114. If the motor is in the high fire position when this shift is made, a return energization circuit will be completed through wire 122, switch 115, switch 108 (high fire), and the wire 117, whereby the motor will run to move valve 104 to low fire and open switch 108, closing switch 107. Such opening of switch 108 stops the motor and it will remain in this low fire condition of adjustment until switch 114 and switch 103 areclosed to start another heating cycle. If the motor was already at the low fire setting upon start of the cooling cycle, switch 108 will be open and there is no closed circuit to complete energization of the motor. 'It will also be apparent that the temperature controller is efiectively disabled during the cooling cycle due to the open condition of switch 114, so that actuation of such controller cannot result in the burner being turned to the high fire setting, even though there would naturally be a demand for heat.

Accordingly, when another heating cycle is commenced, the burner will initially be supplied only the reduced flow of fuel for safe ignition. There is an inherent time lag in the drive of the modulating valve by the motor from one position to another and such delay is sufficient for the fuel to be ignited before the full supply condition is reached. The cycle shifting switches 103, 114 and 115 are not only ganged but preferably operatively linked to the means, such as the air cylinders, employed for adjustment of the flow control dampers \for automatic operation. In one construction, these switches are of pressure type connected in the pneumatic system for operating the dampers, whereby a single operating handle is used to effect all adjustments necessary to shift the oven operation from one cycle to another.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims or the equivalent of such be em,- ployed.

We, therefore, particularly point out and distinctly claim as our invention:

l. A mold drying and cooling oven comprising walls defining a work-receiving chamber, supply and collector ducts in and communicating with said chamber, a fan, air-conducting means connecting the outlet and inlet of said fan respectively to said supply and collector ducts, heating means located in said air-conducting means at the inlet side of said fan, thereby to provide a drying cycle of operation in which air is drawn from the oven chamber and returned thereto after being heated, a damper-controlled intake for atmospheric air in said airconducting means between said heating means and the fan inlet, a first exhaust duct connected to and extending upwardly relative to said collector duct, damper means for closing the air-conducting means in advance of the heating means and opening the collector duct to said first exhaust duct, whereby a cooling cycle can be established by opening said damper-controlled intake and operating said damper means as aforesaid to by-pass the heating means and circulate atmospheric air through the oven chamber and out said first exhaust duct, and a second exhaust duct communicating with the chamber of less capacity than said first duct for continuously exhausting a relatively small proportion of air from the chamber to the atmosphere.

2. A mold drying and cooling oven comprising walls defining a work-receiving chamber, supply and collector ducts in and communicating with said chamber, a fan, air conducting means connecting the outlet and inlet of said fan respectively to said supply and collector ducts, heating means located in said air-conducting means at the inlet side of said fan, thereby to provide a drying cycle of operation in which air is drawn from the oven chamber and returned thereto after being heated, a dampercontrolled intake for atmospheric air in said air-conducting means between said heating means and the fan inlet, an oven exhaust duct connected to and extending upwardly relative to said collector duct, and damper means for closing the air-conducting means in advance of the heating means and opening the collector duct to said exhaust duct, whereby a cooling cycle can be established by opening said damper-control1ed intake and operating said damper means as aforesaid to by-pass the heating means and circulate atmospheric air through the oven chamber and out said exhaust duct.

3. A mold drying and cooling oven comprising top and side walls forming a work-receiving chamber, a ceiling duct in said chamber having a plurality of downwardly directed discharge nozzles, a fan having its outlet connected to said ceiling duct, a collector duct in communication with said chamber, an oven exhaust vent, means selectively operative to connect said collector duct to the inlet of said fan or to said oven exhaust vent, said means including a source of heat in the connection of the collector duct to the fan, means actuatable to supply fresh air to the fan inlet, the collector duct being placed in communication with the fan to establish a drying cycle of operation in which air from the chamber is drawn past said heat source and recirculated by the fan, cooling of the work after heating in such cycle being provided by venting the collector duct and actuating the last-named means to admit fresh air to the fan, and a separate exhaust fan operative to expel a relatively small proportion of air from the chamber.

4. In a mold drying and cooling oven including a fan operative to discharge air in the work receiving compartment thereof, a flow connection having an oven air intake in the compartment and extending to the inlet of said fan, a heater in such connection, a fresh air intake in the connection between the heater and the fan, an exhaust stack in the connection between the oven air intake and the heater, and closures for said fresh air intake and exhaust stack, both the fresh air intake and exhaust stack being closed during the heating cycle to place the oven under negative pressure and recirculate air therewithin past the heater, and both being opened for the cooling cycle in which the heater is by-passed and air exhausted from the oven by the positive pressure produced therein by the fan.

5. In a mold drying and cooling oven including a fan operative to discharge air in the work-receiving compartment thereof, a flow connection having an oven air intake in the compartment and extending to the inlet of said fan, a heater in such connection, a fresh air intake in the connection between the heater and the fan, a stack joined to the connection between the oven air intake and the heater, a closure for said fresh air intake and a damper at the junction of the stack and flow connection at the 10 heater side thereof to close one or the other, the fresh air intake and stack being closed during the heating cycle of the oven and opened in the cooling cycle, with the flow connection closed to the heater in the latter condition.

6. In a mold drying and cooling oven having an enclosure which includes a top wall, a central supply duct within said enclosure against the ceiling thereof and having bottom discharge orifices, collector duct means arranged about said ceiling duct and being open for escape of oven air into the same, an external housing at the top of the oven forming a mixing chamber above the supply duct and at least a portion of the collector duct, a fan in said mixing chamber having its outlet connected through the oven roof to the central supply duct, a heater in the mixing chamber, a damper-controlled passage from the said portion of the collector duct to the chamber, a stack connected to another portion of the collector duct and having a damper therein to open and close the same, and a door in such external housing openable to admit atmospheric air to the mixing chamber, said passage from the collector duct to the chamber being opened and the stack and door closed during the heating cycle of oven operation, the passage being closed and the door and stack opened to circulate fresh air through the oven in the cooling cycle.

7. In a mold drying and cooling oven including a fan operative to discharge air in the work-receiving compartment thereof, a return flow connection between the compartment and the fan including a heater, said heater having a burner unit equipped with fuel regulating means, temperature responsive means for controlling said fuel regulating means in accordance with the oven temperature, damper means for opening said retuun flow connection to the atmosphere at both sides of said heater to by-pass the same for cooling of the heated work, and control circuit means for disabling said temperature responsive means and maintaining the fuel regulating means in a low condition of adjustment when said damper means are thus operated to establish a cooling cycle of operation.

8. In a mold oven, means including a combustion heater for circulating heated air through the oven in a work drying cycle of operation, means for thereafter flowing relatively cool air through the oven to provide a cooling cycle for reducing the work temperature before removal, fuel supply means for said heater, means for opening and closing the fuel supply respectively in such heating and cooling cycles, flow modulating means in the fuel supply means operative to regulate the delivery to the heater between low and high positions of adjustment, first circuit means including temperature responsive means for actuating said flow modulating means in accordance with oven temperature, second circuit means for controlling said flow modulating means, and cycle control means for placing the flow modulating means under control of either of the first or second circuit means, the latter being operative to move the flow modulating means to the low position of adjustment if not in this condition upon shifting of the control thereto from the first circuit means.

References Cited in the file of this patent UNITED STATES PATENTS 2,012,115 Woodruff Aug. 20, 1935 2,385,962 Barnett Oct. 2, 1945 2,779,105 Park Jan. 29, 1957 2,834,699 Rusciano May 13, 1958 FOREIGN PATENTS 123,769 Great Britain Oct. 2, 1919 

